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= DevFaqLookupWhere
:jbake-type: wiki
:jbake-tags: wiki, devfaq, needsreview
:jbake-status: published
:keywords: Apache NetBeans wiki DevFaqLookupWhere
:description: Apache NetBeans wiki DevFaqLookupWhere
:toc: left
:toc-title:
:syntax: true

=== What uses Lookup?

There are a number of places link:DevFaqLookup.asciidoc[Lookup ] is commonly found/used in NetBeans.  Generally, if you have found some class and you are wondering where on earth you get an actual instance of one of those, the answer is probably "from something-or-other's Lookup".

Common cases:

* `Lookup.getDefault()()` - you want to find some global singleton or all instances of a particular object link:DevFaqLookupDefault.asciidoc[registered in the system]
* `Project.getLookup()` - provides objects specific to a project.  The typical pattern is, you have used FileOwnerQuery to get the Project that owns some file, and now you want to find something like the classpath (from the Project's ClassPathProvider, which lives in its Lookup)
* `link:DevFaqWhatIsANode.asciidoc[Node.getLookup()]` - this is how you get things like syntax trees, open and save interfaces and other miscellaneous stuff from Nodes representing files or other things
* `link:DevFaqWindowsTopComponent.asciidoc[TopComponent.getLookup()]` - if you are writing a UI component, and want to affect the global selection, but your component doesn't display nodes and you don't have any use for Nodes, you probably want to provide your own Lookup here with whatever you want to include in it (things like link:http://www.netbeans.org/download/dev/javadoc/org-openide-nodes/org/openide/cookies/OpenCookie.html[OpenCookie], link:http://www.netbeans.org/download/dev/javadoc/org-openide-nodes/org/openide/cookies/SaveCookie.html[SaveCookie], objects your other UI code may want to track if you're doing a master-detail view, etc.)
* `link:http://www.netbeans.org/download/dev/javadoc/org-openide-util/org/openide/util/Utilities.html#actionsGlobalContext()[Utilities.actionsGlobalContext()]` returns a `Lookup` which represents the global "selection context" in NetBeans.  It is a `ProxyLookup` which proxies the lookup of whichever `link:DevFaqWindowsTopComponent.asciidoc[TopComponent]` currently has focus.  So if you listen for changes in the presence or absence of a particular type in this lookup, you will receive appropriate changes whenever the backing `Lookup` being proxied changes.

=== Apache Migration Information

The content in this page was kindly donated by Oracle Corp. to the
Apache Software Foundation.

This page was exported from link:http://wiki.netbeans.org/DevFaqLookupWhere[http://wiki.netbeans.org/DevFaqLookupWhere] , 
that was last modified by NetBeans user Admin 
on 2009-11-06T15:52:48Z.


*NOTE:* This document was automatically converted to the AsciiDoc format on 2018-02-07, and needs to be reviewed.